Mr. Michael S. “Mike” Rogers is the substitute teacher for the day, but he is having trouble deciphering the secret message that was left for him by the teacher. Mr. Rogers knows the note is in English, but that’s about all. Can you help him? ENCRYPTED.txt
Frequency analysis.
From the name, we can tell it uses a substitution cipher. We can use a substitution solver like quipqiup.com to help us to solve it.
Here is your flag: only_slightly_better_than_caesar